Fibromyalgia (FMS), defined as the presence of both chronic widespread pain and the finding of 11/18 tender points on examination, affects 2% of the general population. Drug therapy for FMS is largely symptomatic as there is not yet a complete understanding of the pathogenesis of the disease. In the past 17 years, supervised aerobic exercise has emerged as an important treatment modality to improve pain, aerobic capacity, function and well-being. Individuals who are able to adhere to exercise almost always maintain the symptomatic benefits of exercise. Unfortunately, the rate of exercise adherence six months after the completion of a well-structured supervised exercise program is disappointingly low. Furthermore, although the efficacy of supervised aerobic exercise in the research setting is well documented, the applicability of such intervention in the clinic setting is doubtful. Therefore, we propose to conduct the Research to Encourage Exercise for Fibromyalgia (REEF), a randomized attention-controlled trial whose primary Aim is to evaluate the efficacy of telephone-delivered motivational interviewing (Ml) to encourage exercise, in improving exercise adherence and self-report physical function (co-primary outcome measures) for FMS patients. REEF will enroll 200 FMS patients, randomizing them to either the Ml group or the attention-control (AC) group. Participants from each group will receive a total of six telephone calls within a 12-week period. Prior to the phone calls, participants from both groups will receive an individualized exercise prescription and two supervised exercise training sessions to get them started on an exercise program. All subjects will undergo comprehensive outcome assessment at baseline, week 12, week 24 and week 36. The secondary Aim of this application is to determine the mediators between Ml and improvement in self-report physical function. The proposed research is significant because our focus is the promotion of adherence to an exercise program, of adequate intensity, in order to maximize functioning and well-being for patients with FMS. The use of a predominantly home-based exercise program and telephone-delivered Ml by a trained licensed practice nurse (LPN) could potentially make the proposed intervention more accessible to the greater majority of FMS patients. Furthermore, if proven efficacious, Ml could readily be applied to other chronically painful conditions (e.g. chronic back pain).